Question

Is one copy of a public static variable created for each AppDomain in a process or is it just one copy for the whole process? In other words if I change the value of a static variable from within one AppDomain, will it affect the value of the same static variable within another AppDomain in the same process?

Answer 1

It is per application domain as proven by this example:

public class Foo
{
    public static string Bar { get; set; }
}

public class Test
{
    public Test()
    {
        Console.WriteLine("Second AppDomain: {0}", Foo.Bar);
    }
}

class Program
{
    static void Main()
    {
        // Set some value in the main appdomain
        Foo.Bar = "bar";
        Console.WriteLine("Main AppDomain: {0}", Foo.Bar);

        // create a second domain
        var domain = AppDomain.CreateDomain("SecondAppDomain");

        // instantiate the Test class in the second domain
        // the constructor of the Test class will print the value
        // of Foo.Bar inside this second domain and it will be null
        domain.CreateInstance(Assembly.GetExecutingAssembly().FullName, "Test");
    }
}